Geographic Range

Speckled swimming crabs, Arenaeus cribrarius, are found on the Atlantic coast of North, Central and South America, ranging from the state of Massachusetts in the United States to Uruguay. (Tavares, 2009)

Habitat

Speckled swimming crabs live along sandy beaches in shallow to deep water up to 68 m in depth. They have been found in waters 11 to 28.6 °C in temperature and 27.5 to 35 PSU in salinity. When on land, they prefer the foreshore area of beaches in fine mixed sands with low organic matter. (Edlin Guerra-Castro and Carmona-Suárez, 2007; Tavares, 2009)

Physical Description

The carapace of speckled swimming crabs is twice as wide as it is long and can be as wide as 154 mm. The carapace ranges in color from light reddish brown to olive brown and is covered with many small, rounded white spots. The chelipeds (claws) are short and narrow. They have 4 pairs of short, broad pereopods (walking legs) with yellow tips. The fifth pair of pereopods is flattened and paddle-shaped. The perepods and the lower surface of the carapace are densely covered with hair. Speckled swimming crabs can weigh as much as 45 g. (Tavares, 2009)

Development

Speckled swimming crabs have 4 main stages of life; they begin as
planktonic zoea, become megalops, benthic juveniles, and finally adults. Speckled swimming crabs pass through 8 stages as zoea, each lasting 4 to 6 days. After each stage, they molt and develop into the next stage of zoea. The body of zoea primarily consists of the head. They have a single dorsal spine in the middle of the head and a long rostrum extending downward beneath the eyes. Zoea also have a long abdomen. Megalops resemble a tiny lobster. During this stage, the head slightly elongates, the dorsal spine, located posterior to the head, shortens, they eyes become stalked, and small chelipeds develop. The abdomen remains long and has now developed prominent peropods. After 13 days, megalops metamorphose into a juvenile crab, with a prominent carapace with two lateral spines projecting from the outer edges. Juveniles have larger chelipeds and a flattened pair of 5th peropods. If juveniles successfully survive, they eventually become adult crabs. (Stuck and Truesdale, 1988)

Reproduction

Between molting periods, male speckled swimming crabs express a courtship display to attract premolted females. The display intensifies when a potential mate is visually recognized. After a female is chosen, the male grasps the female with his chelipeds and holds her under himself for 25 to 35 days until the female molts. Soon after the female molts, when her shell is still soft, the male inverts her so they are positioned abdomen to abdomen. He penetrates her with specially-modified pleopods, transferring spermatophore packages into her gonopores. After copulation, he continues to carry her for 24 to 36 days until her shell has hardened completely. Speckled swimming crabs are polygynandrous, meaning males and females have multiple mates. (Pinheiro and Fransozo, 1999)

Speckled swimming crabs breed year-round, although breeding is more common in the summer and winter, when water temperature oscillations are reduced. Females can produce between 135,000 and 682,000 eggs. Like other members of the family Portunidae, speckled swimming crabs communicate during the reproductive period, which can occur through visual, acoustic, chemical and tactile cues. Speckled swimming crabs reach sexual maturity when their carapace is between 60 and 64 mm in width, which generally occurs around 60 to 80 days of age. (Pinheiro and Franosozo, 1998; Pinheiro and Fransozo, 1999; Pinheiro and Fransozo, 2002; Pinheiro and Terceiro, 2000)

Speckled swimming crabs breed year-round, but breeding is more common in summer and winter.

Range number of offspring

135,000 to 682,000

Range age at sexual or reproductive maturity (female)

60 to 80 days

Range age at sexual or reproductive maturity (male)

60 to 80 days

After copulation, female speckled swimming crabs extrude fertilized eggs and carry the egg mass beneath her abdomen with specially-modified pleopods. Females protect their egg mass and fan it with their pleopods to oxygenate the developing eggs and keep them clean. After larvae hatch and are released into the water column, there is no further parental care. (Pinheiro and Fransozo, 1999)

Lifespan/Longevity

There is currently little information available regarding the lifespan of speckled swimming crabs.

Behavior

Speckled swimming crabs are nocturnal and solitary, coming together with other members of their species only to breed. When threatened, they automatically assume a defensive position with their chelipeds raised up in the air. Speckled swimming crabs migrate between shallower and deeper waters as they forage and evade predators. (Edlin Guerra-Castro and Carmona-Suárez, 2007; Frick, 2003)

Home Range

Communication and Perception

As with other crustaceans, speckled swimming crabs communicate through visual, acoustic, chemical and tactile cues. The associated senses are also used in perceiving the environment. (Pinheiro and Fransozo, 1999)

Food Habits

Speckled swimming crabs primarily eat detritus from the ocean floor. They also eat crustaceans, fish, and molluscs. Like most crabs, speckled swimming crabs are opportunistic scavengers, and they have even been recorded chasing down, capturing, and preying on hatchling loggerhead sea turtles. Speckled swimming crabs bury themselves near the breaker zone and ambush prey that crawl or swim near them, seizing the prey with their chelipeds. Crabs then rebury themselves, which may help to subdue captured prey. (Carmona-Suárez and Conde, 2005; Frick, 2003)

Predation

The only known predators of speckled swimming crabs other than humans are two species of sea turtles: loggerhead sea turtles and Kemp's Ridley sea turtles. The camouflaged pattern on their carapace helps to conceal speckled swimming crabs in the sand from predators. Also useful against predators are two strong, sharp, slightly upcurved spines on the side of the body. Additionally, the front edge of their carapace is serrated. Speckled swimming crabs are least vulnerable to predation when fully grown, when their spines and camoflouging pattern are fully developed. (Frick, 2003; Tavares, 2009)

Economic Importance for Humans: Positive

Economic Importance for Humans: Negative

There are no known adverse effects of speckled swimming crabs on humans.

Conservation Status

Speckled swimming crabs have not been evaluated by the IUCN or the US Fish and Wildlife Service. They are, however, commercially gathered in Brazil which likely influences population sizes. (Carmona-Suárez and Conde, 2002)

Contributors

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Neotropical

living in the southern part of the New World. In other words, Central and South America.

acoustic

uses sound to communicate

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

biodegradation

helps break down and decompose dead plants and/or animals

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.